Production of diesel fuel from renewable feedstocks containing phosphorus

ABSTRACT

A process has been developed for producing diesel fuel from renewable feedstocks such as plant oils, animal oils and greases. The process involves treating a renewable feedstock by hydrogenating and deoxygenating to provide a diesel boiling range fuel hydrocarbon product. If desired, the hydrocarbon product can be isomerized to improve cold flow properties. A portion of the hydrocarbon product is recycled to the treatment zone to increase the hydrogen solubility of the reaction mixture. The renewable feedstock comprises from about 1 to about 20 wt. ppm phosphorus measured as elemental phosphorus.

CROSS-REFERENCE TO RELATED APPLICATION

This applications claims priority from Provisional Application Ser. No.61/076,605 filed Jun. 27, 2008, the contents of which are herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to a process for producing diesel boiling rangehydrocarbons useful as fuel from renewable feedstocks such as theglycerides and free fatty acids found in materials such as plant oils,animal oils, animal fats, and greases. The process involveshydrogenation, decarboxylation, decarbonylation, and/orhydrodeoxygenation and hydroisomerization in two or more steps. Theprocess is operated with a volume ratio of recycle product to feedstockfrom about 2:1 to about 8:1. The process is operated at a total pressureof from about 1379 kPa absolute (200 psia) to about 4826 kPa absolute(700 psia). The renewable feedstock contains from about 1 to about 20wt. ppm phosphorous.

BACKGROUND OF THE INVENTION

As the demand for diesel boiling range fuel increases worldwide there isincreasing interest in sources other than petroleum crude oil forproducing diesel fuel. One such source is what has been termed renewablesources. These renewable sources include, but are not limited to, plantoils such as corn, rapeseed, canola, soybean and algal oils, animal fatssuch as tallow, fish oils and various waste streams such as yellow andbrown greases and sewage sludge. The common feature of these sources isthat they are composed of glycerides and Free Fatty Acids (FFA). Both ofthese classes of compounds contain aliphatic carbon chains having fromabout 8 to about 24 carbon atoms. The aliphatic carbon chains in theglycerides or FFAs can be fully saturated or mono-, di-, orpoly-unsaturated. Phosphorus is a common contaminant in these types offeedstocks.

There are reports in the art disclosing the production of hydrocarbonsfrom oils. For example, U.S. Pat. No. 4,300,009 discloses the use ofcrystalline aluminosilicate zeolites to convert plant oils such as cornoil to hydrocarbons such as gasoline and chemicals such as para-xylene.U.S. Pat. No. 4,992,605 discloses the production of hydrocarbon productsin the diesel boiling range by hydroprocessing vegetable oils such ascanola or sunflower oil. Finally, US 2004/0230085 A1 discloses a processfor treating a hydrocarbon component of biological origin byhydrodeoxygenation followed by isomerization.

Applicants have developed a process which comprises two or more steps tohydrogenate, decarboxylate, decarbonylate, and/or hydrodeoxygenate andthen hydroisomerize the feedstock, and which can be successfullyoperated when the feedstock contains from about 1 to about 20 wt. ppm ofphosphorus. Employing a volume ratio of recycle hydrocarbon to feedstockranging from about 2:1 to about 8:1 additionally serves to dilute thephosphorus that is in the feedstock and also provides a mechanism toincrease the hydrogen solubility in the reaction mixture sufficiently sothat the operating pressure of the process may be lowered. The range ofsuccessful volume ratios of recycle to feedstock is based upon thedesired hydrogen solubility in the reaction mixture. The reaction zonemay be operated at a pressure in the range of about 1379 kPa absolute(200 psia) to about 4826 kPa absolute (700 psia).

SUMMARY OF THE INVENTION

The process is for producing a hydrocarbon fraction useful as a dieselboiling range fuel or fuel blending component from a renewable feedstockwherein the renewable feedstock comprises from about 1 to about 20 wt.ppm phosphorus. The process comprises treating the renewable feedstock,including the 1 to about 20 wt. ppm phosphorus, in a reaction zone byhydrogenating and deoxygenating the renewable feedstock at reactionconditions to provide a reaction product comprising a hydrocarbonfraction comprising n-paraffins useful as a diesel boiling range fuel,or fuel blending component. A portion of hydrocarbon fraction isrecycled to the reaction zone wherein the volume ratio of recycle tofeedstock is in the range of about 2:1 to about 8:1. The hydrogenationand deoxygenation reaction product, without employing steps to removephosphorus, is isomerized to provide an isomerized reaction product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general flow scheme of one embodiment of the invention.

FIG. 2 is a more detailed flow scheme of one embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

As stated, the present invention relates to a process for producing ahydrocarbon stream useful as diesel boiling range fuel from renewablefeedstocks such as those feedstocks originating from plants or animals.The term renewable feedstock is meant to include feedstocks other thanthose derived from petroleum crude oil. The renewable feedstocks thatcan be used in the present invention include any of those which compriseglycerides and free fatty acids (FFA). Most of the glycerides will betriglycerides, but monoglycerides and diglycerides may be present andprocessed as well. Examples of these renewable feedstocks include, butare not limited to, canola oil, corn oil, soy oils, rapeseed oil,soybean oil, colza oil, tall oil, sunflower oil, hempseed oil, oliveoil, linseed oil, coconut oil, castor oil, peanut oil, palm oil, mustardoil, cottonseed oil, jatropha oil, tallow, yellow and brown greases,lard, train oil, fats in milk, fish oil, algal oil, sewage sludge, andthe like. Additional examples of renewable feedstocks include non-ediblevegetable oils from the group comprising Jatropha curcas (Ratanjoy, WildCastor, Jangli Erandi), Madhuca indica (Mohuwa), Pongamia pinnata(Karanji Honge), and Azadiracta indicia (Neem). The glycerides and FFAsof the typical vegetable or animal fat contain aliphatic carbon chainsin their structure which have about 8 to about 24 carbon atoms, with amajority of the fats and oils containing a high concentration of 16 and18 carbon atom chains. Mixtures or co-feeds of renewable feedstocks andpetroleum derived hydrocarbons may also be used as the feedstock. Otherfeedstock components which may be used, especially as a co-feedcomponent in combination with the above listed feedstocks, include,spent motor oils and industrial lubricants, used paraffin waxes, liquidsderived from the gasification of coal, biomass, natural gas followed bya downstream liquefaction step such as Fischer-Tropsch technology(including pyrolysis oils), liquids derived from depolymerization,thermal or chemical, of waste plastics such as polypropylene, highdensity polyethylene, and low density polyethylene; and other syntheticoils generated as byproducts from petrochemical and chemical processes.Mixtures of the above feedstocks may also be used as co-feed components.One advantage of using a co-feed component is the transformation of mayhave been considered to be a waste product from a petroleum based orother process into a valuable co-feed component to the current process.

Renewable feedstocks that can be used in the present invention maycontain a variety of impurities. For example, tall oil is a by productof the wood processing industry and tall oil contains esters and rosinacids in addition to FFAs. Rosin acids are cyclic carboxylic acids. Therenewable feedstocks may also contain contaminants such as alkalimetals, e.g. sodium and potassium, phosphorous as well as solids, waterand detergents. Phosphorus can be problematic as it may be present inthe form of phospholipids which can form gums and plug the pre-heatersand reactors. An optional first step is to remove at least some of thesecontaminants. One possible pretreatment step involves contacting therenewable feedstock with an ion-exchange resin in a pretreatment zone atpretreatment conditions. The ion-exchange resin is an acidic ionexchange resin such as Amberlyst™-15 and can be used as a bed in areactor through which the feedstock is flowed through, either upflow ordownflow. Another possible means for removing contaminants is a mildacid wash. This is carried out by contacting the feedstock with an acidsuch as sulfuric, nitric or hydrochloric acid in a reactor. The acid andfeedstock can be contacted either in a batch or continuous process.Contacting is done with a dilute acid solution usually at ambienttemperature and atmospheric pressure. If the contacting is done in acontinuous manner, it is usually done in a counter current manner. Yetanother possible means of removing metal contaminants from the feedstockis through the use of guard beds which are well known in the art. Thesecan include alumina guard beds either with or without demetallationcatalysts such as nickel or cobalt. Filtration and solvent extractiontechniques are other choices which may be employed. Hydroprocessing suchas that described in U.S. Ser. No 11/770,826 is another pretreatmenttechnique which may be employed.

However, pretreatment techniques add cost to the overall process andfrom an economic perspective, it is desirable to minimize their use. Onthe other hand, higher purity feedstocks that do not need pretreatmentare generally more costly than those with higher levels of contaminants.For example crude and refined vegetable oils are significantly morecostly than tallow and greases, but tallow and greases contain greaterquantities of impurities. The present process takes advantage of thelower cost feedstocks which contain phosphorus, while at the same time,minimizes the use of pretreatment techniques. The feedstock to thepresent invention may contain up to about 20 wt. ppm phosphorus,measured as elemental phosphorus. In another embodiment, the renewablefeedstock may contain from about 10 to about 20 wt. ppm phosphorusmeasured as elemental phosphorus. This allows for lower cost, lessrefined, feedstocks to be utilized. Pretreatment techniques are alsominimized since only phosphorus in excess of 20 wt. ppm needs to beremoved.

The renewable feedstock, containing from about 1 to about 20 wt. ppm ofphosphorus, measured as elemental phosphorus, is flowed to a reactionzone comprising one or more catalyst beds in one or more reactors. Theterm feedstock is meant to include feedstocks that have not been treatedto remove contaminants as well as those feedstocks purified in apretreatment zone to remove phosphorus in excess of about 20 wt. ppm.Feedstocks containing phosphorus in excess of 20 wt. ppm formed gums inthe pre-heater or in the reactor which lead to plugging of thepre-heater or the reactor. However, feedstocks containing less than 20wt. ppm phosphorus did not cause gum formation in the pre-heater or inthe reactor, see the example below.

In the reaction zone, the renewable feedstock is contacted with ahydrogenation or hydrotreating catalyst in the presence of hydrogen athydrogenation conditions to hydrogenate the olefinic or unsaturatedportions of the n-paraffinic chains. Hydrogenation or hydrotreatingcatalysts are any of those well known in the art such as nickel ornickel/molybdenum dispersed on a high surface area support. Otherhydrogenation catalysts include one or more noble metal catalyticelements dispersed on a high surface area support. Non-limiting examplesof noble metals include Pt and/or Pd dispersed on gamma-alumina.Hydrogenation conditions include a temperature of about 200° C. to about300° C. and a pressure of about 1379 kPa absolute (200 psia) to about4826 kPa absolute (700 psia). Other operating conditions for thehydrogenation zone are well known in the art.

The hydrogenation and hydrotreating catalysts enumerated above are alsocapable of catalyzing decarboxylation, decarbonylation, and/orhydrodeoxygenation of the feedstock to remove oxygen. Decarboxylation,decarbonylation, and hydrodeoxygenation are herein collectively referredto as deoxygenation reactions. Decarboxylation and decarbonylationconditions include a relatively low pressure of about 3447 kPa (500psia) to about 6895 kpa (1000 psia), a temperature of about 288° C. toabout 345° C. and a liquid hourly space velocity of about 1 to about 4hr⁻¹. Since hydrogenation is an exothermic reaction, as the feedstockflows through the catalyst bed the temperature increases anddecarboxylation and hydrodeoxygenation will begin to occur. Thus, it isenvisioned and is within the scope of this invention that all threereactions occur simultaneously in one reactor or in one bed.Alternatively, the conditions can be controlled such that hydrogenationprimarily occurs in one bed and decarboxylation and/orhydrodeoxygenation occurs in a second bed. Of course if only one bed isused, then hydrogenation occurs primarily at the front of the bed, whiledecarboxylation, decarbonylation and hydrodeoxygenation occurs mainly inthe middle and bottom of the bed. Finally, desired hydrogenation can becarried out in one reactor, while decarboxylation, decarbonylation,and/or hydrodeoxygenation can be carried out in a separate reactor.

Hydrogen is a reactant in the reactions above, and to be effective, asufficient quantity of hydrogen must be in solution to most effectivelytake part in the catalytic reaction. Past processes have operated athigh pressures in order to achieve a desired amount of hydrogen insolution and readily available for reaction. If hydrogen is notavailable at the reaction site of the catalyst, the coke forms on thecatalyst and deactivates the catalyst. To solve this problem, thepressure is often raised to insure enough hydrogen is available to avoidcoking reactions on the catalyst. However, higher pressure operationsare more costly to build and to operate as compared to their lowerpressure counterparts. One advantage of the present invention is theoperating pressure is in the range of about 1379 kPa absolute (200 psia)to about 4826 kPa absolute (700 psia) which is lower than that found inother previous operations. In another embodiment the operating pressureis in the range of about 2413 kPa absolute (350 psia) to about 4481 kPaabsolute (650 psia), and in yet another embodiment operating pressure isin the range of about 2758 kPa absolute (400 psia) to about 4137 kPaabsolute (600 psia). Furthermore, the rate of reaction is increasedresulting in a greater amount of throughput of material through thereactor in a given period of time. Lower operating pressures provide anadditional advantage in increasing the decarboxylation reaction whilereducing the hydrodeoxygenation reaction. The result is a reduction inthe amount of hydrogen required to remove oxygen from the feedstockcomponent and produce a finished product. Hydrogen can be a costlycomponent of the feed and reduction of the hydrogen requirements isbeneficial from an economic standpoint.

The desired amount of hydrogen is kept in solution at lower pressures byemploying a large recycle of hydrocarbon. Other processes have employedhydrocarbon recycle in order to control the temperature in the reactionzones since the reactions are exothermic reactions. However, the rangeof recycle to feedstock ratios used herein is set based on the need tocontrol the level of hydrogen in the liquid phase and therefore reducethe deactivation rate. The amount of recycle is determined not ontemperature control requirements, but instead, based upon hydrogensolubility requirements. Hydrogen has a greater solubility in thehydrocarbon product than it does in the feedstock. By utilizing a largehydrocarbon recycle the solubility of hydrogen in the liquid phase inthe reaction zone is greatly increased and higher pressures are notneeded to increase the amount of hydrogen in solution and avoid catalystdeactivation at low pressures. In one embodiment of the invention, thevolume ratio of hydrocarbon recycle to feedstock is from about 2:1 toabout 8:1 or from about 2:1 to about 6:1. In another embodiment theratio is in the range of about 3:1 to about 6:1 and in yet anotherembodiment the ratio is in the range of about 4:1 to about 5:1. Thedetermination of the ranges of suitable volume ratios of hydrocarbonrecycle is shown in U.S.A No. 60/973,797, hereby incorporated byreference in its entirety.

Another benefit of the recycle ratio employed is that the recyclematerial operates to dilute the amount of phosphorus that is present inthe reaction mixture. While the feedstock may contain up to about 20 wt.ppm phosphorus, the feedstock is mixed with the hydrocarbon recycleeffectively diluting the concentration of phosphorus in the reactionmixture. With the feedstock being limited to less than about 20 wt. ppmphosphorus, and then being diluted with the hydrocarbon recycle, thephosphorus containing compounds do not form gums in the pre-heater or inthe reactor. Furthermore, the resulting concentration of phosphorus inthe reaction mixture can be tolerated by the catalyst in thehydrogenation and deoxygenation zone. The hydrogenation anddeoxygenation catalyst appears to remove the phosphorus from thereaction mixture without severely deactivating the catalyst. Even thoughthe feedstock contained up to about 20 wt. ppm phosphorus, and gums werenot formed in the pre-heaters or in the reactor, the effluent of thehydrogenation and deoxygenation reactor contains little phosphorus.Therefore it is not necessary to remove phosphorus from thehydrogenation and deoxygenation zone effluent before passing theeffluent to the isomerization zone.

The reaction product from the deoxygenation reactions in thedeoxygenation zone will comprise a liquid portion and a gaseous portion.The liquid portion comprises a hydrocarbon fraction which is essentiallyall n-paraffins and having carbon numbers in the range of C8 to aboutC24. Different feedstocks will result in different distributions ofparaffins. A portion of this hydrocarbon fraction, after separation, maybe used as the hydrocarbon recycle described above. Although thishydrocarbon fraction is useful as a diesel boiling range fuel, or a fuelblending component, because it comprises essentially all n-paraffins, itwill have poor cold flow properties. To improve the cold flow propertiesof the liquid hydrocarbon fraction, the liquid hydrocarbon fraction iscontacted with an isomerization catalyst under isomerization conditionsto at least partially isomerize the n-paraffins to branched paraffinssuch as isoparaffins. Catalysts and conditions for isomerization arewell known in the art. See for example US 2004/0230085 A1 which isincorporated by reference in its entirety. Isomerization can be carriedout in a separate bed of the same reaction zone, i.e. same reactor,described above or the isomerization can be carried out in a separatereactor.

The product of the hydrogenation and deoxygenation reaction zone iscontacted with an isomerization catalyst in the presence of hydrogen atisomerization conditions to isomerize the normal paraffins to branchedparaffins. Only minimal branching is required, enough to overcomecold-flow problems of the normal paraffins. Since attempting forsignificant branching runs the risk of high degree of undesiredcracking, the predominant isomerized product is a mono-branchedhydrocarbon.

The isomerization of the paraffinic product can be accomplished in anymanner known in the art or by using any suitable catalyst known in theart. Suitable catalysts comprise a metal of Group VIII (IUPAC 8-10) ofthe Periodic Table and a support material. Suitable Group VIII metalsinclude platinum and palladium, each of which may be used alone or incombination. The support material may be amorphous or crystalline.Suitable support materials include amorphous alumina, amorphoussilica-alumina, ferrierite, ALPO-31, SAPO-11, SAPO-31, SAPO-37, SAPO-41,SM-3, MgAPSO-31, FU-9, NU-10, NU-23, ZSM-12, ZSM-22, ZSM-23, ZSM-35,ZSM-48, ZSM-50, ZSM-57, MeAPO-11, MeAPO-31, MeAPO-41, MeAPSO-11,MeAPSO-31, MeAPSO41, MeAPSO-46, ELAPO-11, ELAPO-31, ELAPO-41, ELAPSO-11,ELAPSO-31, ELAPSO-41, laumontite, cancrinite, offretite, hydrogen formof stillbite, magnesium or calcium form of mordenite, and magnesium orcalcium form of partheite, each of which may be used alone or incombination. ALPO-31 is described in US 4,310,440. SAPO-11, SAPO-31,SAPO-37, and SAPO-41 are described in U.S. Pat. No. 4,440,871. SM-3 isdescribed in U.S. Pat. No. 4,943,424; U.S. Pat. No. 5,087,347; U.S. Pat.No. 5,158,665; and U.S. Pat. No. 5,208,005. MgAPSO is a MeAPSO, which isan acronym for a metal aluminumsilicophosphate molecular sieve, wherethe metal Me is magnesium (Mg). Suitable MeAPSO-31 catalysts includeMgAPSO-31. MeAPSOs are described in U.S. Pat. No. 4,793,984, and MgAPSOsare described in U.S. Pat. No. 4,758,419. MgAPSO-31 is a preferredMgAPSO, where 31 means a MgAPSO having structure type 31. Many naturalzeolites, such as ferrierite, that have an initially reduced pore sizecan be converted to forms to suitable for olefin skeletal isomerizationby removing associated alkali metal or alkaline earth metal by ammoniumion exchange and calcination to produce the substantially hydrogen form,as taught in U.S. Pat. No. 4,795,623 and U.S. Pat. No. 4,924,027.Further catalysts and conditions for skeletal isomerization aredisclosed in U.S. Pat. No. 5,510,306, U.S. Pat. No. 5,082,956, and U.S.Pat. No. 5,741,759.

The isomerization catalyst may also comprise a modifier selected fromthe group consisting of lanthanum, cerium, praseodymium, neodymium,samarium, gadolinium, terbium, and mixtures thereof, as described inU.S. Pat. No. 5,716,897 and U.S. Pat. No. 5,851,949. Other suitablesupport materials include ZSM-22, ZSM-23, and ZSM-35, which aredescribed for use in dewaxing in U.S. Pat. No. 5,246,566 and in thearticle entitled “New molecular sieve process for lube dewaxing by waxisomerization,” written by S. J. Miller, in Microporous Materials 2(1994) 439-449. The teachings of U.S. Pat. No. 4,310,440; U.S. Pat. No.4,440,871; U.S. Pat. No. 4,793,984; U.S. Pat. No. 4,758,419; U.S. Pat.No. 4,943,424; U.S. Pat. No. 5,087,347; U.S. Pat. No. 5,158,665; U.S.Pat. No. 5,208,005; U.S. Pat. No. 5,246,566; U.S. Pat. No. 5,716,897;and U.S. Pat. No. 5,851,949 are hereby incorporated by reference.

U.S. Pat. No. 5,444,032 and U.S. Pat. No. 5,608,134 teach a suitablebifunctional catalyst which is constituted by an amorphoussilica-alumina gel and one or more metals belonging to Group VIIIA, andis effective in the hydroisomerization of long-chain normal paraffinscontaining more than 15 carbon atoms. U.S. Pat. No. 5,981,419 and U.S.Pat. No. 5,968,344 teach a suitable bifunctional catalyst whichcomprises: (a) a porous crystalline material isostructural withbeta-zeolite selected from boro-silicate (BOR—B) andboro-alumino-silicate (Al—BOR—B) in which the molar SiO₂:Al₂O₃ ratio ishigher than 300:1; (b) one or more metal(s) belonging to Group VIIIA,selected from platinum and palladium, in an amount comprised within therange of from 0.05 to 5% by weight. Article V. Calemma et al., App.Catal. A: Gen., 190 (2000), 207 teaches yet another suitable catalyst.

The isomerization catalyst may be any of those well known in the artsuch as those described and cited above. Isomerization conditionsinclude a temperature of about 150° C. to about 360° C. and a pressureof about 1724 kPa absolute (250 psia) to about 4726 kPa absolute (700psia). In another embodiment the isomerization conditions include atemperature of about 300° C. to about 360° C. and a pressure of about3102 kPa absolute (450 psia) to about 3792 kPa absolute (550 psia).Other operating conditions for the isomerization zone are well known inthe art.

The final effluent stream, i.e. the stream obtained after all reactionshave been carried out, is now processed through one or more separationsteps to obtain a purified hydrocarbon stream useful as a diesel boilingrange fuel or fuel blending component. Because the final effluent streamcomprises both a liquid and a gaseous component, the liquid and gaseouscomponents are separated using a separator such as a cold separator. Theseparated liquid component comprises the product hydrocarbon streamuseful as a diesel fuel. Further separations may be performed to removenaphtha and LPG from the product hydrocarbon stream. The separatedgaseous component comprises mostly hydrogen and the carbon dioxide fromthe decarboxylation reaction. The carbon dioxide can be removed from thehydrogen by means well known in the art, reaction with a hot carbonatesolution, pressure swing absorption, etc. Also, absorption with an aminein processes such as described in co-pending applications U.S.A No.60/093,792 and U.S.A No. 60/973,816, hereby incorporated by reference,may be employed. If desired, essentially pure carbon dioxide can berecovered by regenerating the spent absorption media. The hydrogenremaining after the removal of the carbon dioxide may be recycled to thereaction zone where hydrogenation primarily occurs and/or to anysubsequent beds/reactors.

Finally, a portion of the product hydrocarbon is recycled to thehydrogenating and deoxygenating reaction zone. The recycle stream may betaken from the product hydrocarbon stream after the hydrogenating anddeoxygenating reactor(s) and separation form gaseous components, andrecycled back to the hydrogenating and deoxygenating reactor(s). Or therecycle stream may be taken from the effluent of a separation unit, suchas a hot high pressure separator, located between the deoxygenationreaction zone and the isomerization reaction zone. Although possible, itis less preferred to take the recycle stream from the isomerized productsince isomerized products are more susceptible to cracking than thenormal paraffins in the hydrogenating and deoxygenating reaction zone. Aportion of a hydrocarbon stream from, for example, a hot high pressureseparator or a cold high pressure separator, may also be cooled down ifnecessary and used as cool quench liquid between the beds of thedeoxygenation reaction zone to further control the heat of reaction andprovide quench liquid for emergencies. The recycle stream may beintroduced to the inlet of the deoxygenation reaction zone and/or to anysubsequent beds or reactors. One benefit of the hydrocarbon recycle isto control the temperature rise across the individual beds. However, asdiscussed above, the amount of hydrocarbon recycle herein is determinedbased upon the desired hydrogen solubility in the reaction zone.Increasing the hydrogen solubility in the reaction mixture allows forsuccessful operation at lower pressures, and thus reduced cost.Operating with high recycle and maintaining high levels of hydrogen inthe liquid phase helps dissipate hot spots at the catalyst surface andreduces the formation of undesirable heavy components which lead tocoking and catalyst deactivation. Furthermore, high hydrocarbon recycleoperates to dilute the phosphorus in the feedstock and avoid formationof gums which plug pre-heaters and the reactor.

The following embodiment is presented in illustration of this inventionand is not intended as an undue limitation on the generally broad scopeof the invention as set forth in the claims. First an embodiment isdescribed in general as with reference to FIG. 1. Then an embodiment isdescribed in more detail with reference to FIG. 2.

Turning to FIG. 1 renewable feedstock 102 enters deoxygenation reactionzone 104 along with recycle hydrogen 126. Renewable feedstock containsfrom about 1 to about 20 wt. ppm phosphorus, measured as elementalphosphorus. Deoxygenated product 106 is stripped in hot high pressurehydrogen stripper 108 using hydrogen 114 a. Carbon oxides and watervapor are removed with hydrogen in overhead 110. Selectively strippeddeoxygenated product is passed to isomerization zone 116 along withrecycle hydrogen 126 a and make-up hydrogen 114 b. Isomerized product118 is combined with overhead 110 and passed to product recovery zone120. Carbon oxide stream 128, light ends stream 130, water byproductstream 124, hydrogen stream 126, and branched paraffin-rich product 122are removed from product recover zone 120. Branched paraffin-richproduct 122 may be collected for use as diesel fuel and hydrogen stream126 is recycled to the deoxygenation reaction zone 104.

Turning to FIG. 2, the process begins with a renewable feedstock stream2 which may pass through an optional feed surge drum. Renewablefeedstock stream 2 contains from about 1 to about 20 ppm phosphorus,measured as elemental phosphorus. The feedstock stream is combined withrecycle gas stream 68 and recycle stream 16 to form combined feed stream20, which is heat exchanged with reactor effluent and then introducedinto deoxygenation reactor 4. The heat exchange may occur before orafter the recycle is combined with the feed. Deoxygenation reactor 4 maycontain multiple beds shown in FIG. 2 as 4 a, 4 b and 4 c. Deoxygenationreactor 4 contains at least one catalyst capable of catalyzingdecarboxylation and/or hydrodeoxygenation of the feedstock to removeoxygen. Deoxygenation reactor effluent stream 6 containing the productsof the decarboxylation and/or hydrodeoxygenation reactions is removedfrom deoxygenation reactor 4 and heat exchanged with stream 20containing feed to the deoxygenation reactor. Stream 6 comprises aliquid component containing largely normal paraffin hydrocarbons in thediesel boiling range and a gaseous component containing largelyhydrogen, vaporous water, carbon monoxide, carbon dioxide and propane.

Deoxygenation reactor effluent stream 6 is then directed to hot highpressure hydrogen stripper 8. Make up hydrogen in line 10 is dividedinto two portions, stream 10 a and 10 b. Make up hydrogen in stream 10 ais also introduced to hot high pressure hydrogen stripper 8. In hot highpressure hydrogen stripper 8, the gaseous component of deoxygenationreactor effluent 6 is selectively stripped from the liquid component ofdeoxygenation reactor effluent 6 using make-up hydrogen 10 a and recyclehydrogen 28. The dissolved gaseous component comprising hydrogen,vaporous water, carbon monoxide, carbon dioxide and at least a portionof the propane, is selectively separated into hot high pressure hydrogenstripper overhead stream 14. The remaining liquid component ofdeoxygenation reactor effluent 6 comprising primarily normal paraffinshaving a carbon number from about 8 to about 24 with a cetane number ofabout 60 to about 100 is removed as hot high pressure hydrogen stripperbottom 12.

A portion of hot high pressure hydrogen stripper bottoms forms recyclestream 16 and is combined with renewable feedstock stream 2 to createcombined feed 20. Another portion of recycle stream 16, optional stream16 a, may be routed directly to deoxygenation reactor 4 and introducedat interstage locations such as between beds 4 a and 4 b and/or betweenbeds 4 b and 4 c in order, or example, to aid in temperature control.The remainder of hot high pressure hydrogen stripper bottoms in stream12 is combined with hydrogen stream 10 b to form combined stream 18which is routed to isomerization reactor 22. Stream 18 may be heatexchanged with isomerization reactor effluent 24.

The product of the isomerization reactor containing a gaseous portion ofhydrogen and propane and a branched-paraffin-rich liquid portion isremoved in line 24, and after optional heat exchange with stream 18, isintroduced into hydrogen separator 26. The overhead stream 28 fromhydrogen separator 26 contains primarily hydrogen which may be recycledback to hot high pressure hydrogen stripper 8. Bottom stream 30 fromhydrogen separator 26 is air cooled using air cooler 32 and introducedinto product separator 34. In product separator 34 the gaseous portionof the stream comprising hydrogen, carbon monoxide, hydrogen sulfide,carbon dioxide and propane are removed in stream 36 while the liquidhydrocarbon portion of the stream is removed in stream 38. A waterbyproduct stream 40 may also be removed from product separator 34.Stream 38 is introduced to product stripper 42 where components havinghigher relative volatilities are separated into stream 44 with theremainder, the diesel range components, being withdrawn from productstripper 42 in line 46. Stream 44 is introduced into fractionator 48which operates to separate LPG into overhead 50 leaving a naphthabottoms 52. Any of optional lines 72, 74, or 76 may be used to recycleat least a portion of the isomerization zone effluent back to theisomerization zone to increase the amount of n-paraffins that areisomerized to branched paraffins.

The vapor stream 36 from product separator 34 contains the gaseousportion of the isomerization effluent which comprises at least hydrogen,carbon monoxide, hydrogen sulfide, carbon dioxide and propane and isdirected to a system of amine absorbers to separate carbon dioxide andhydrogen sulfide from the vapor stream. Because of the cost of hydrogen,it is desirable to recycle the hydrogen to deoxygenation reactor 4, butit is not desirable to circulate the carbon dioxide or an excess ofsulfur containing components. In order to separate sulfur containingcomponents and carbon dioxide from the hydrogen, vapor stream 36 ispassed through a system of at least two amine absorbers, also calledscrubbers, starting with the first amine absorber zone 56. The aminechosen to be employed in first amine scrubber 56 is capable ofselectively removing at least both the components of interest, carbondioxide and the sulfur components such as hydrogen sulfide. Suitableamines are available from DOW and from BASF, and in one embodiment theamines are a promoted or activated methyldiethanolamine (MDEA). See U.S.Pat. No. 6,337,059, hereby incorporated by reference in its entirety.Suitable amines for the first amine absorber zone from DOW include theUCARSOL™ AP series solvents such as AP802, AP804, AP806, AP810 andAP814. The carbon dioxide and hydrogen sulfide are absorbed by the aminewhile the hydrogen passes through first amine scrubber zone and intoline 68 to be recycled to the first reaction zone. The amine isregenerated and the carbon dioxide and hydrogen sulfide are released andremoved in line 62. Within the first amine absorber zone, regeneratedamine may be recycled for use again. The released carbon dioxide andhydrogen sulfide in line 62 are passed through second amine scrubberzone 58 which contains an amine selective to hydrogen sulfide, but notselective to carbon dioxide. Again, suitable amines are available fromDOW and from BASF, and in one embodiment the amines are a promoted oractivated MDEA. Suitable amines for the second amine absorber zone fromDOW include the UCARSOL™ HS series solvents such as HS101, HS102, HS103,HS104, HS115. Therefore the carbon dioxide passes through second aminescrubber zone 58 and into line 66. The amine may be regenerated whichreleases the hydrogen sulfide into line 60. Regenerated amine is thenreused, and the hydrogen sulfide may be recycled to the deoxygenationreaction zone. Conditions for the first scrubber zone includes atemperature in the range of 30 to 60° C. The first absorber is operatedat essentially the same pressure as the reaction zone. By “essentially”it is meant that the operating pressure of the first absorber is withinabout 1034 kPa absolute (150 psia) of the operating pressure of thereaction zone. For example, the pressure of the first absorber is nomore than 1034 kPa absolute (150 psia) less than that of the reactionzone. The second amine absorber zone is operated in a pressure range offrom 138 kPa absolute (20 psia) to 241 kPa absolute (35 psia). Also, atleast the first the absorber is operated at a temperature that is atleast 1° C. higher than that of the separator. Keeping the absorberswarmer than the separator operates to maintain any light hydrocarbons inthe vapor phase and prevents the light hydrocarbons from condensing intothe absorber solvent.

The following examples are presented in illustration of this inventionand are not intended as undue limitations on the generally broad scopeof the invention as set out in the appended claims.

EXAMPLE

Several renewable feedstocks, each having different levels of phosphoruswere hydrogenated and deoxygenated (some were also isomerized), and theoccurrence of plugging in the pre-heater or in the reactors was noted.Some of the experiments were conducted with a hydrocarbon recycle andsome of the experiments were conducted without a hydrocarbon recycle.The renewable feedstocks tested included vegetable oils, grease, andtallow. For all cases except the yellow grease, the beef tallow, and thecooking oil, the feedstocks were processed at 1 LHSV with respect tofresh feedstock in a down-flow trickle bed reactor containing 150 cc ofa promoted nickel-molybdenum on alumina catalyst. The feedstocks werecontinuously added at a rate of 150 cc/hr or 1LHSV over a period of 1000hours at an operating pressure of about 3447 kPa absolute (500 psia) andabout 310 to about 332° C. (590 to 650° F.). The H2/hydrocarbon ratio inthe feed was about 3700 to about 5000 scfb.

The Table shows the different renewable feedstocks, the concentration ofphosphorus in the renewable feedstock in wt. ppm measured as elementalphosphorus, the hydrocarbon recycle to feedstock volume ratio, and theoccurrence of plugging in the pre-heater or in a reactor. Pluggingincludes a stoppage or reduction in fluid flow through the pre-heater orreactor, or may be indicted by a high pressure drop across thepre-heater or reactor.

TABLE Plugging of Phosphorus, Hydrocarbon Recycle to Pre-HeaterFeedstock wt. ppm Feedstock Volume Ratio or Reactor Soybean Oil 5 NoHydrocarbon Recycle No Palm Oil 0.3 No Hydrocarbon Recycle No CookingOil None detected No Hydrocarbon Recycle No Canola Oil 0.7 4:1 No CanolaOil 41 4:1 Yes Jatropha Oil 0.1 4:1 No Yellow Grease 30 No HydrocarbonRecycle Yes Beef Tallow 80 No Hydrocarbon Recycle Yes Beef Tallow 16 4:1No Beef Tallow 15 4:1 No Beef Tallow 5 4:1 No

1) A process for producing a diesel boiling range hydrocarbon product from a renewable feedstock comprising; a) treating the renewable feedstock in a reaction zone by hydrogenating and deoxygenating the feedstock at reaction conditions to provide a reaction product comprising paraffins having from about 8 to about 24 carbon atoms, and recycling a portion of the reaction product to the reaction zone wherein the volume ratio of recycle to feedstock is in the range of about 2:1 to about 8:1, wherein the renewable feedstock comprises from about 1 to about 20 wt. ppm phosphorus, measured as to elemental phosphorus; and b) isomerizing at least a portion of the paraffins in the reaction product in an isomerization zone by contacting with an isomerization catalyst at isomerization conditions to isomerize at least a portion of the paraffins to branched-paraffins. 2) The process of claim 1 wherein the renewable feedstock comprises from about 10 to about 20 wt. ppm phosphorus, measured as elemental phosphorus. 3) The process of claim 1 wherein the volume ratio of recycle to feedstock is in the range of about 2:1 to about 6:1. 4) The process of claim 1 wherein the volume ratio of recycle to feedstock is in the range of about 4:1. 5) The process of claim 1 further comprising pre-treating the renewable feedstock in a pretreatment zone at pretreatment conditions to remove phosphorus in excess of about 20 wt. ppm, measured as elemental phosphorus. 6) The process of claim 1 where the feedstock is hydrogenated and deoxygenated by contacting the feedstock with a hydrogenation and deoxygenation catalyst at a temperature of about 200° C. to about 300° C. and a pressure of about 1379 kPa absolute (200 psia) to about 4826 kPa absolute (700 psia). 7) The process of claim 1 wherein the reaction product is passed to the isomerization zone without employing phosphorus removal techniques. 8) The process of claim 1 where deoxygenation comprises at least one of decarboxylation, decarbonylation, and hydrodeoxygenation. 9) The process of claim 1 further comprising treating a petroleum hydrocarbon feedstock in the reaction zone. 10) The process of claim 1 wherein the renewable feedstock comprises at least one component selected from the group consisting of canola oil, corn oil, soy oil, rapeseed oil, soybean oil, colza oil, tall oil, sunflower oil, hempseed oil, olive oil, linseed oil, coconut oil, castor oil, peanut oil, palm oil, mustard oil, cottonseed oil, jatropha oil, tallow, yellow and brown greases, lard, train oil, fats in milk, fish oil, algal oil, sewage sludge. 11) The process of claim 10 wherein the renewable feedstock further comprises at least one co-feed component selected from the group consisting of spent motor oils, spent industrial to lubricants, used paraffin waxes, liquids derived from the gasification of coal, biomass, natural gas followed by a downstream liquefaction step, liquids derived from depolymerization, thermal or chemical, of waste plastics, and synthetic oils generated as byproducts from petrochemical and chemical processes. 